1. Technical Field
The disclosure contained herein generally relates to a method for monitoring image content and adjusting the interval or frequency of process control sampling and maintenance cycles correspondingly.
2. Description of Related Art
The electrophotographic print process has become widely used due to its capability for high print performance, high print quality and low page costs. Much effort has been made to further improve the process, especially in relation to increased printing speed and decreased printing costs. Issues related to print speed and costs may be affected by the physical mechanisms behind the process. Although the following discussion will be made in relation to the xerographic process, other processes are envisioned, such as laser printing, LED printing, ink jet printing, phase-charge or solid ink printing, dye sublimation printing, or thermal printing.
Xerography, also called electrophotography, is a method of dry photocopying in which the image is transferred by use of the attractive forces of electric charges. A beam of light, such as from a laser or a linear array of photodiodes, is made to strike the original material, e.g., a white page with black or color lettering or images. Light rays are reflected off the white areas onto a photosensitive plate over which electric charges have been spread often referred to as the photoreceptor. The charge collected by each photodiode or by the laser is proportional to the reflectance of each area of the paper. A reflectance map of the image on the paper may be built up in a single sweep. Color images can be captured by exposing the image with colored light or by using colored filters in the linear array. Charges are neutralized from the areas struck by the rays. Since no light rays are reflected from black lettering for example, charges are retained on the plate in areas corresponding to the lettered areas of the original. A printing material referred to as toner is introduced that sticks to the charged areas. A sheet of paper is then passed between the plate and another charged object that draws the toner from the plate to the paper, forming an image of the original. The toner is then fused to the paper with heat.
Many of the components of a xerographic print engine may need periodic maintenance or calibration procedures to maintain high quality print output. Print engines, which as used herein may include xerographic, inkjet, or other devices that print text and graphics on a document, make use of process control cycles to sample the particular internal states and/or outputs of the system and to make the appropriate updates to system actuators to maintain a consistent level of output print performance. In addition to process control cycles, many print engines require a particular set of actions to be taken during the transition from the standby or ready state to the printing state (“cycle-up”). These cycle-up activities could actually include running process control cycles as well as other maintenance cycles. Print engines might require maintenance cycles to be performed at regular intervals during a user's print job in order to continue printing with the highest level of output print quality. These maintenance cycles may also be required when a sensor reading drifts out of specification limits. In a general context, the rules or the algorithms that describe these required actions and their occurrence are referred to as the “printer operations” or “printing procedure” for the printing engine.
From a user perspective, the cycles spent in running process control, cycle-up, or maintenance cycles are, in fact, wasted cycles. Here, “wasted” refers to the fact that no user output pages are being produced during these cycles. Thus, these cycles contribute to the run cost of the print engine through abuse of components, waste of toner, and other print related expenses, but do not produce any useable output for the user.
In the past, the update period for the process control sampling has typically been fixed at design time. Likewise, the set of activities that is required during the cycle-up routine is either fixed at design time or may be set to vary based on the state of the machine or specific environmental factors. Maintenance cycles have traditionally been performed based on a fixed interval between cycles or based on feedback from a sensor in the machine. Thus, in the past there has not typically been a provision for modifying the printing procedure based on the image or job content of the user's submitted print jobs in an effort to improve system run cost. Currently, some machines do provide a provision for a “draft” mode and/or an “enhanced” mode of operation. However, these are user input preferences that are used to determine the required operational mode for the print engine. These strategies do not take into account within-job or job-to-job image content variations as part of the construction of the printing procedure.
Accordingly, what is needed is a method to monitor image content and adjust the interval or frequency of process control sampling and maintenance cycles correspondingly. More specifically, there is a need for a method to reduce the run cost per page for a printing engine based on the print job image content.
The disclosure contained herein describes solutions to one or more of the problems described above.